The field of olefin transformation has been widely studied and is the subject of a number of patents. Particularly important processes are those which enable long chain oligomers to be produced. Depending on the number of carbon atoms in the chain, such oligomers have applications in the chemicals and petrochemicals industries, or are components of gasoline. The reactions which are of interest in the present invention are dimerization, co-dimerization or oligomerization of olefins.
The prior art contains numerous patents. Of those, we shall describe patents in which the catalysis reaction is carried out in a homogeneous liquid phase with a soluble catalyst, or heterogeneous catalysis is carried out with a solid catalyst. Such processes have disadvantages, however: the catalysts usedxe2x80x94often nickel basedxe2x80x94are expensive. Solid catalysts deactivate by the action of pollutants, and they must be regularly regenerated or replaced. For soluble catalysts, the outlet effluent contains catalyst which must be separated out, involving unavoidable supplemental expense. In addition to the degree of conversion, which varies depending on the olefin to be treatedxe2x80x94for n-butenes, the maximum degree of conversion of economic interest is 80% xe2x80x94, the reaction is generally not sufficiently selective; finally, a mixture of products is obtainedxe2x80x94which is not always desirablexe2x80x94and which must be separated out.
The present invention uses a sequence of processes to carry out dimerization, co-dimerization or oligomerizing olefins in two steps. In the remainder of the text, the term xe2x80x9coligomerizationxe2x80x9d covers these three types of reactions.
The first step is catalytic oligomerization which may be of the homogeneous liquid phase type or of the heterogeneous type. The term xe2x80x9cheterogeneous catalysis reactionxe2x80x9d used in this text defines a reaction where two phases co-exist, the catalyst being solid. The second step is catalysis in a two-phase medium where the catalyst is dissolved in a polar phase which is not miscible with the organic phase containing at least one olefin. Among the advantages of this invention are a large increase in the reaction yield, and an increase in selectivity, so the reaction can be better oriented towards the species which are to be obtained. The second step of the reaction is particularly selective for dimers, which is the species which is most frequently desired. The invention also enables the pollutants present in the apparatus to be closely controlled, as any pollutants present in the initial feed will have been partially eliminated in the first step. If necessary, they can also be completely eliminated by an intermediate treatment. In a particular implementation of the invention, catalyst wastage can be reduced by better use of the catalyst in the two-phase medium. The first step of the process is thus homogeneous catalysis in which at least part of the catalyst is recovered with the effluent. The catalyst is then used in the liquid-liquid two-phase catalysis step.
Processes for homogeneous liquid phase catalysis or heterogeneous catalysis can convert feeds containing olefins, particular propylene or n-butenes. These processes can treat feeds containing 50% to 100% by weight of olefins, usually 70% to 90% by weight. However, these processes are not limited to the treatment of these feeds alone, in particular it has been verified that they also work for feeds containing olefins with a carbon chain containing two, five or six carbon atoms. For feeds containing less than 50% by weight of olefins, in particular for propylene or n-butenes, the consumption of catalyst or the size of the reactors renders the process less economical, the costs being higher as the feed becomes more diluted and the olefin less reactive. Similarly, the cost is large for olefins with a carbon chain containing more than four carbon atoms, which is why such homogeneous liquid phase catalysis or heterogeneous catalysis processes are particularly suitable for olefins containing three or four carbon atoms. Further, the selectivity for dimersxe2x80x94which is the product which is most in demandxe2x80x94strictly depends on conversion: for butenes, it does not exceed 85% for a feed converted in an amount of 80% by weight. The liquid-liquid two-phase process can convert dilute feeds, i.e., containing less than 50% by weight of olefins, and can also produce a higher selectivity for dimers, this selectivity possibly reaching 95%; further, this liquid-liquid two-phase process renders the conversion to dimers less dependent on the starting feed.
Prior art heterogeneous catalysis processes which can be used in the first step of the invention use catalysts containing a metal, preferably nickel, on a to support which can, for example, be alumina, silica, silica-alumina, a zeolite or a silico-aluminate. The reaction temperature is about 10xc2x0 C. to 250xc2x0 C., the pressure being such that the feed remains liquid. French patent French application No. 2,608,594 describes a process for dimerizing olefins using heterogeneous catalysts comprising nickel compounds deposited on alumina. The heterogeneous catalysis catalysts in the first step of the invention can also be a mineral compound alone, the mineral compound being, for example, a silico-aluminate, a zeolite or a silica-alumina. IFP Enterprises markets a silica-alumina compound under trade reference IP501, for example.
Prior art descriptions concerning homogeneous liquid phase processes propose the use of different types of catalysts depending on the olefins to be treated and also depending on the product which is particularly desired, those catalysts all containing at least one compound of a metal, preferably nickel, and an alkoylaluminium halide. The reaction temperature is about xe2x88x9240xc2x0 C. to +100xc2x0 C., the pressure is such that the reactants are at least partially, normally mainly in the liquid phase and the stirring conditions are those necessary to convert at least a portion of the feed.
For oligomerization, in particular dimerization and trimerization, of olefins, United States patent U.S. Pat. No. 4,316,851 recommends the use of mixed nickel compounds with general formula (R1COO)(R2COO)Ni where R1 is an alkyl, cycloalkyl, alkenyl, aryl, aralkyl or alkaryl residue, for example, containing at least 5 carbon atoms, preferably an alkyl residue containing 5 to 20 carbon atoms, this residue possibly being substituted by hydroxyl groups, for example, and R2 is a halogenoalkyl residue containing 1 to 3 carbon atoms, with formula CmHpXq where m=1, 2 or 3, p equals zero or a whole number and q is a whole number, with the condition that p+q=2m+1. R2 is preferably a halogenomethyl residue CXnH3xe2x88x92n where X is fluorine, chlorine, bromine or iodine, and n is a whole number from 1 to 3.
The preparation of catalysts for dimerization or co-dimerizing C2, C3 or C4 olefins is also well known, the catalysts resulting, for example, from the interaction of halides of xcfx80-allyl nickel phosphine with Lewis acids (French application No. 1,410,430), from the interaction of halides of nickel phosphine with Lewis acids (U.S. Pat. No. 3,485,881) or from the interaction of certain nickel carboxylates with alkylaluminium halides (U.S. Pat. No. 3,321,546). Similarly, U.S. Pat. No. 4,404,415 describes dimerizing propylene to higher oligomers: nonenes or mixtures of nonenes and dodecenes, the type of catalyst used being a complex in which a metal, preferably nickel, is bonded to at least one unsaturated hydrocarbon residue, which may or may not be substituted, for example a bis-xcfx80-allyl nickel, a xcfx80-allyl nickel halide or bis-cyclooctadiene nickel associated with a halogenated aluminum compound. A further catalyst type is constituted by complexes formed by mixing at least one nickel compound with at least one alkylaluminum compound and possibly a ligand, for example a phosphine. A preferred class of catalysts comprises catalysts obtained by mixing at least one nickel carboxylate (the carboxylate residue containing at least six carbon atoms) with at least one dichloroalkylaluminum or alkylaluminum sesquichloride, the Al/Ni atomic ratio being in the range 2:1 to 50:1.
However, depending on the impurities present in the feeds to be treated, difficulties in industrial implementation may be encountered. Such difficulties have been overcome in part by using catalysts with improved catalytic formulae incorporating at least one divalent nickel compound with at least one alkylaluminium halide and at least one organic Brxc3x8nsted acid (U.S. Pat. No. 4,283,305) or a mixed compound of nickel in association with an alkylaluminum compound (U.S. Pat. Nos. 4,316,851; 4,366,087; and 4,389,049). These improved catalytic formulae usually include a halogenocarboxylic acid, the corresponding anion or a carboxylic acid anhydride as in the case of U.S. Pat. No. 4,362,650. In addition to extolling the virtues of the catalysts described above, U.S. Pat. No. 5,059,571 proposes to overcome the difficulties of implementing the process by using a catalyst comprising at least one divalent nickel compound with at least one alkylaluminium halide and at least one epoxy compound.
A further type of catalyst used exhibits good results for dimerizing butenes and is described in U.S. Pat. No. 4,716,239 as the association of an inorganic divalent nickel compound (for example a carbonate, bicarbonate, or a basic carbonate (hydroxycarbonate), a hydroxide (or oxide) with a halogenoacetic acid (for example monochloroacetic acid, monofluoroacetic acid, dichloroacetic acid, trichloroacetic acid, difluoroacetic acid or trifluoroacetic acid) in a carboxylic acid ester with general formula R1COOR2 where R1 and R2 are each a linear or branched alkyl group containing 1 to 5 carbon atoms, R1 also possibly being hydrogen. Such esters of acids can, for example, be methyl acetate, methyl formate, n-butyl acetate, isobutyl acetate, methyl propionate, or isopropyl formate.
The subject matter of our invention is a two-step process. When the first step involves catalysis in a homogeneous phase reaction zone, one of the catalysts described above is used. The catalyst selected depends on the olefin to be treated and on the product which is to be obtained in the majority. However, the first step can also be oligomerization by heterogeneous phase catalysis. In this type of catalysis, nickel compounds deposited on mineral supports or the supports alone are generally used. Such catalysts have the disadvantage, however, of being less selective for dimers, in particular when conversion is high, the amount of trimers and tetramers possibly representing over 30% of the products. Thus the invention described in French application No. 2,608,594 is a process for producing improved catalysts comprising nickel compounds deposited on alumina. One advantage of supported catalysis processes is that the solid catalyst remains in the reactor, and the problem of separating the catalyst from the effluent does not have to be addressed. In contrast, it cannot be used as a catalyst in the second step in the sequence of processes of the invention, as is possible when a soluble catalyst is used for homogeneous liquid phase catalysis.
The second step of the process of the invention is two-phase catalysis where the catalyst is dissolved in a polar phase which is not miscible with the organic phase containing the olefins.
These catalytic reactions in a two-phase medium are carried out at a temperature of less than +100xc2x0 C., for example between xe2x88x9250xc2x0 C. and +100xc2x0 C., the pressure being kept between 0.01 and 20 MPa, with the highest pressures being used for ethylene.
The documents cited above, in particular French patent French application No. 2,611,700, describe the use of liquids with an ionic nature, compositions of which we shall describe below, used as solvents for the organometallic nickel complexes for olefin dimerization. The use of such media which are only very slightly miscible with aliphatic hydrocarbons enables the homogeneous catalysts to be put to better use. In order to carry out these oligomerizations, the olefin is brought into contact with the polar phase containing the nickel complex and contact between the phases is ensured by energetic stirring. At the end of the reaction, the phases are separated by any suitable means, for example the mixture is allowed to settle and the upper phase, which includes the dimers, co-dimers and oligomers, is extracted. The medium can also be supplied continuously and the phase containing the dimers and oligomers can be extracted continuously, taking care to provide a zone within the reactor which enables the two liquid phases to be separated out. Olefins which can be treated by this type of process are, for example, ethylene, propylene, 1- and 2-butenes, styrene, pentenes or mixtures of these compounds.
Among the different compositions of the polar phase and dimerization, co-dimerization and oligomerization catalytic compositions are the examples in the following patents: French application No. 2,611,700 concerns a medium with an ionic nature, liquid at the usual dimerization temperatures, which comprises at least one aluminum halide and at least one quaternary ammonium halide. The nickel complexes which are known for dimerizing, co-dimerizing and oligomerizing olefins and which are soluble in the media with an ionic nature can be neutral zero-valent, monovalent or divalent complexes, these latter must contain at least one nickel-carbon or nickel-hydrogen bond, or ionic complexes containing a nickel-carbon or nickel-hydrogen bond. The description in U.S. Pat. No. 5,104,840 has a non aqueous liquid composition with an ionic nature resulting from bringing at least one alkoylaluminium dihalide into contact with at least one quaternary ammonium halide and/or at least quaternary phosphonium halide. The composition is liquid below about +80xc2x0 C., for example between about xe2x88x9270xc2x0 C. and about +40xc2x0 C. The compounds in the composition can be mixed in any order. The mixture can be made by simply bringing the compounds into contact followed by stirring, until a homogeneous liquid phase is obtained. The mixture can also advantageously be made in the presence of a saturated aliphatic hydrocarbon solvent which dissolves the alkoylaluminium dihalide(s), for example, in this case, after producing two clear liquid phases, the supernatant phase containing essentially the hydrocarbon solvent is eliminated in order to allow only the liquid composition to subsist. Any nickel complex can be used as a catalyst in a composition with an ionic nature. U.S. Pat. No. 5,550,306 and U.S. Pat. No. 5,502,018 describe processes for dimerization, codimerization and oligomerizing olefins, in particular propylene, but these processes can be used on ethylene, n-butenes and n-pentenes, alone or as a mixture, pure or diluted by an alkane, such as those found in cuts from oil refining processes such as catalytic cracking or steam cracking. In the process for dimerization, co-dimerization and oligomerizing at least one olefin, the compounds are brought into contact in any order. The reaction temperature can be in the range xe2x88x9240xc2x0 C. to +70xc2x0 C., preferably in the range xe2x88x9220xc2x0 C. to +50xc2x0 C., the pressure can be in the range from atmospheric pressure to 20 MPa, preferably in the range from atmospheric pressure to 5 MPa. The composition described in U.S. Pat. No. 5,550,306 results from dissolving a nickel compound mixed or complexed with at least one tertiary phosphine, at least partially dissolved in a liquid mixture with an ionic nature of a quaternary ammonium halide and/or a quaternary phosphonium halide, an aluminium halide, an aromatic hydrocarbon and possibly an alkylaluminium. More precisely, the catalytic composition comprises at least one nickel compound mixed or complexed with at least one tertiary phosphine, at least partially dissolved in a medium with an ionic nature resulting from bringing at least one aluminium halide into contact with at least one quaternary ammonium halide and/or at least one quaternary phosphonium halide and with at least one aromatic hydrocarbon. The composition described in U.S. Pat. No. 5,502,018 results from mixing one equivalent of a divalent nickel complex containing two molecules of a tertiary phosphine with one equivalent of a divalent nickel complex containing neither water nor phosphine. The mixture of two types of nickel compounds must necessarily be associated with an alkylaluminium halide, the mixture being used in conventional implementations of the reaction, i.e., without solvent or in the presence of a halogenated or non halogenated hydrocarbon. These mixtures are particularly useful in the liquid compositions with an ionic nature which are formed by quaternary ammonium halides, and/or quaternary phosphonium halides with aluminium halides and possibly aromatic hydrocarbons. The latest research described in French application No. 2,736,562 regarding processes for oligomerizing olefins in a two-phase medium have a catalytic composition comprising a mixture of a lithium halide, an alkylaluminium halide and at least one compound of a catalytic element, in particular a nickel complex, and at least one hydrocarbon phase. This mixture has the advantage of being liquid at the start of the reaction and of gradually being transformed into a solid which can easily be separated from the hydrocarbon phase. The olefins to which the process can be applied are, for example, ethylene, propylene, n-butenes, and n-pentenes, alone or as a mixture. The olefin(s) can be used pure or diluted with saturated hydrocarbons such as those found in the cuts from various hydrocarbon refining processes, such as ethane with ethylene, propane with propylene, butanes with butenes. The reaction temperature will be in the range xe2x88x9230xc2x0 C. to +100xc2x0 C., preferably in the range xe2x88x9210xc2x0 C. to +50xc2x0 C. The pressure can be in the range from atmospheric pressure or below atmospheric pressure to 10 MPa, preferably in the range from atmospheric pressure to 1 MPa, but this pressure will be sufficient to keep at least a portion of the olefin or olefins in the liquid phase.
The first catalytic oligomerization step of the process of the invention is preferably liquid phase homogeneous catalysis or heterogeneous catalysis with a solid catalyst. The type of catalysis and the catalyst selected depend on the olefin or olefins to be treated and on the product or products which are to be obtained as the major product. As described above, for homogeneous liquid phase catalysis, the catalytic composition is preferably as follows: the catalyst is a nickel compound or a mixture of nickel compounds, the co-catalyst is an alkyl aluminium or a mixture of alkyl aluminium compounds, or a halogenoalkyl aluminium or a mixture of halogenoalkyl aluminium compounds, or a halogenoacetic acid or a mixture of halogenoacetic acids, and the optional additive to the catalyst may be a compound with an acidic nature, the anion corresponding to that acid, a carboxylic acid ester, an epoxy compound or a phosphine. The catalysts, co-catalysts and possible additives are introduced into the reactor in which the internal temperature is about xe2x88x9240xc2x0 C. to +100xc2x0 C., the pressure is such that the reactants are kept at least partially, usually mainly, in the liquid phase, and the stirring conditions are so as to convert at least a portion of the feed. Energetic mechanical stirring is applied to obtain maximum oligomer conversion. After this first reaction step, the oligomers obtained can be isolated and/or the catalyst can be inhibited and/or the effluent can be washed.